Method of incorporating color couplers in hydrophilic colloids



United States Patent 3,316,094 METHOD OF INCORPORATING COLOR COU- PLERS IN HYDROPHILIC COLLOIDS Aaron Ben-Ezra, Binghamton, N.Y., assignor to General Aniline & Film Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed Mar. 11, 1963, Ser. No. 264,040

4 Claims. (Cl. 96100) This invention relates to a method of incorporating photographic chemical compounds, particularly color couplers in hydrophilic colloids, and especially in lightsensitive silver halide gelatin photographic emulsions.

One of the earliest processes for using color formers in photographic emulsions was suggested in United States Patent 1,055,155 issued to Rudolf Fischer in 1912. Fischer proposed a system of three-layer color photography in which the couplers or color-forming compounds were locate-d in three different emulsion layers; wherein each coupler was capable of yielding, upon reaction with the oxidation products of a primary amino development agent, a dye image in a color complementary to the sensitivity of the layer in which it was incorporated. Although the Fischer process was theoretically feasible, it did not prove successful in practice. The couplers which were then available were not fast to diffusion and tended to migrate from the emulsion layer in which they were incorporated into an adjoining emulsion layer, thus causing a color degradation of the final dye images.

Over the ensuing years, numerous improvements were suggested which deal with modified color formers and techniques for their incorporation in photographic colloids. By synthesizing couplers containing a bulky group, i.e., a long chain alkyl radical (see United States Patent 2,186,849) attached to the molecule, their tendency to diffuse out of their respective sensitive emulsion layers Was greatly reduced. The presence of this group imparts to the molecule a hydrophobic character, These longchain non-diffusing couplers also contain a salt-forming group, i.e., a carboxy or sulfo group which in the form of their alkali salts provides the couplers with watersoluble groups of hydrophilic character to permit their incorporation in aqueous gelatin silver halide emulsions. The simultaneous presence of hydrophilic and hydrophobic groups give these color formers a soap-like character.

While the above process produces excellent dye images free from color degradation, the incorporation into the emulsion of long chain high molecular weight couplers containing salt-forming groups poses a number of difficulties. In most instances, the color formers are dissolved in a water, or water-alcohol solution, of an alkali metal hydroxide such as aqueous sodium hydroxide or alcoholic potassium hydroxide, and then added to the emulsions as a so-called coating final, as one of the last additives just prior to coating.

In most cases there is an extended, but varying, holding time between the addition of the color former solution to the silver halide emulsion and the actual application of the emulsions to the web or the film base. In many instances, there is a time interval between the completion of the remelting and the end of the coating operation which may range between two and six hours.

It is very important that during this holding time the viscosity be held constant, because with the currently used coating techniques, dip-coat, metering or air knife, any variation or drift in viscosity will result in different coating thicknesses. Thus, with a constant coating speed, an emulsion of lower viscosity will produce a thinner layer while a higher viscosity will result in a layer thicker than desire-d. Any change in thickness from standard will result in an unbalanced color picture; the thinner layer will give a lower maximum density, while a heavier layer will produce an undesirable higher maximum density in the layer being coated.

This increase in viscosity on holding and during coating is especially noticeable with emulsion formulations of relatively low water content and relatively high initial viscosity, which contain color formers resistant to diffusion, which are substituted by a water solubilizing group and which are employed in the form of a water soluble alkali metal salt. Surprisingly, the degree of viscosity increase on holding, depends to a large extent on the type of color former used. It is most pronounced with those color formers which contain a benzimidazole nucleus, which is further substituted by a long chain alkyl group attached to one of the nitrogen atoms and a sulfonic or carboxylic acid group.

It is, therefore, an object of this invention to provide a method for the incorporation of color formers in photographic emulsions.

A further object of this invention is to provide a method of incorporating in a hydrophilic photographic colloid, color formers which are stable to diffusion and have an acid group as a substituent.

A further object of the invention involves the uniform distribution of a color former in a liquid photographic gelatin silver halide emulsion while insuring that the viscosity of said silver halide emulsion does not increase materially on holding.

A still further object of this invention comprises a light-sensitive gelatin silver halide emulsion containing a color former uniformly distributed through the gel matrix without the use of an alkali metal hydroxide solvent.

Other objects will be apparent from the following description.

These objects are accomplished by dissolving the chemical compounds, particularly the colorformers fast to diffusion in butyrolactone before adding them to the silver halide emulsion.

In preparing photographic emulsions, the color formers are dissolved in butyrolactone. The butyrolactone solution of the color former is then diluted with water which may also contain some other coating finals. The aqueous butyrolactone solution is then added directly to a melted gelatin silver halide emulsion with adequate stirring. In a second method, the solution of the coupler in butyrolactone is first dissolved in an aqueous solution of a water-soluble colloid such as gelatin and the resulting mixture combined with a melted gelatin silver halide emulsion.

The amount of butyrolactone employed va ies somewhat with different color formers. In general, amounts ranging from 2.5l0.0, and preferably 5.0 parts by weight of butyrolactone per 1.0 part by weight of color former have been found to be most satisfactory.

In preparing the color emulsion for coating, the usual coating aids, stabilizers and wetting agents such as saponin and/or synthetic surfactants which. may be of the anionic, cationic, non-ionic or amphoteric type, are added prior to the addition of the color formers. Among such Wetting agents are those described in United States Patents 1,970,578, 2,118,059, 2,240,476 and 2,768,894.

The color formers which have the strongest tendency to increase the viscosity on holding contain in their molecule, a benzimidazole nucleus which is substituted on the nitrogen atom in thel-position by an alkyl chain of at least 10 carbon atoms and substituted in the 5-position by a water solubilizing group, in which the benzimidazole nucleus is connected through its carbon atom in the 2- position to the residue of a color-forming residue which is reactive with the oxidation products of a primary amino developing agent and contains a reactive methylene or o) phenolic hydroxyl group. These color formers are characterized by the following general formula:

wherein R is a radical containing a reactive methylene, ethenol or phenolic hydroxyl group capable of reacting with the oxidation products or an aromatic amino developing agent to form an azomethine, indoaniline or phenazonium dyestuff, R is an alkyl chain containing at least 10 carbon atoms, e.g., decyl, undecyl, dodecyl, tetradecyl, pentadecyl, hexadecyl, octadecyl and the like, and R is a water solubilizing group such as sulfo, carboxy and the like.

More particularly, color formers which contain a benzirnidazole nucleus as part of the molecule and which are capable of forming dye images upon development with a dialkylamino-aniline developing agent are illustrated by the following structural formulae:

wherein R is a hydroxy aromatic radical, such as substituted or unsubstituted hydroxynaphthyl, hydroxyphenyl and the like in which the hydroxy group is nucleary attached, and said radical being linked to the benzimidazole radical in an ortho-position to said hydroxy group; R is a phenyl radical; R is the grouping -NH--COCH A, in which A is an alkyloyl radical, e.g., acetyl, propionyl, butyryl and the like, and aroyl radical, e.g., benzoyl, naphthoyl and the like or a cyano or a carbethoxy group; n is 1 or 2 and R and R have the same values as above.

Suitable examples of color formers embraced by these general formulae are disclosed in United States Patents 2,545,687 and 2,547,307, in which their method of preparation is also described.

Color formers substituted by a benzimidazole nucleus and capable of forming magenta phenazonium (azine) dye images upon development with t-riaminobenzene developers are described in United States Patent 2,486,440; color formers used with N,N-dialkylphenylenediamine developers are disclosed in United States Patent 2,701,766. They are characterized by the following general formula:

I OH

wherein R R and R have the same values as above; R is hydrogen, a carboxyalkyl, allyl or lower alkyl group; and R is an allyl, lower alkyl, aryl or heterocyclic group.

The invent-ion is further illustrated by the following example, but it is to be understood that the invention is not restricted thereto. The parts and percentages are by weight unless otherwise stated.

EXAMPLE I 200 grams of the yellow color former, 2-(4'-benzoylacetaminophenyl) 1 octadecylbenzimidazole 5 sulfonic acid having the following structural formula:

C rs a1 Hots- Control (Sodium Test (Butyrolactone) Hydroxide) Time (hrs.) Relative Time (hrs.) Relative Viscosity Viscosity It will be noted that the viscosity of the emulsion which contained the color former dissolved in butyrolactone remained substantially constant, whereas the viscosity of the emulsion which contained the sodium hydroxide continued to increase with time.

The emulsion with the butyrolactone solvent was coated onto a base and dried. It gave a coating of even thickness and even maximum density after development. The control emulsion, due to its continued increase in viscosity, showed variations in the developed color densities between the start and the end of the coating.

While the present invention has been described with reference to certain preferred procedures, materials, quantities and uses, it is understood that the invention is not limited thereto, and that numerous variations may be made in the procedure herein described, and that equivalent materials may be substituted. For example, color formers and surface active agents other than those specifically mentioned and utilized in the foregoing examples may be used. Also, the amount of water or of the aqueous solution of a surface active agent may range from 2 to 15 .parts by weight per part of butyrolactone. Accordingly, we do not intend to be limited in the patent granted except as necessitated by the appended claims.

What is claimed is:

11. The method of incorporating in a light-sensitive gelatin halide emulsion, a color former fast to diffusion and capable of forming upon color development with a primary aromatic amino developing agent, a dye image selected from the class consisting of azomethine, indoaniline and phenazonium dye images, said color former containing a benzimidazole nucleus connected through its carbon atoms in the 2-position to the residue of the color-forming molecule which is reactive with the oxidation product of a primary developing agent and which contains a reactive group selected from the class consisting of a reactive methylene and phenolic hydroxy group, said benzimidazole nucleus being substituted on one of the nitrogen atoms by an aliphatic hydrocarbon radical containing at least carbon atoms and substituted in the benzene portion by a water solubilizing group which comprises dissolving said color former in butyrolactone, diluting the resultant solution with an aqueous solution containing a surface active agent and then adding the resultant dispersion to the liquid gelatin silver halide emulsion prior to coating it upon a suitable support.

2. The method of incorporating in a photographic gelatin silver halide emulsion layer, a color former stable to diffusion which is reactive with the oxidation products of a primary amino developing agent to yield upon exposure and development with a primary amino developing agent, a dye image selected from the group consisting of a20- methine, indoaniline and phenazonium dyes, said color former containing a benzimidazole radical characterized by the following general formula:

wherein R is the residue of the color-forming molecule and contains a group selected from the class consisting of reactive methylene and phenolic hydroxy groups capable of reacting with the oxidation products of the primary amino developing agent; R is an aliphatic hydrocarbon radical containing at least 10 carbon atoms; R is a water solubilizing group and the carbon in the 2-position of said benzimidazole radical is linked to the residue of the color-forming molecule which contains a reactive group selected from the group consisting of methylene and phenolic hydroxy groups which comprises dissolving said color former in butyrolactone, diluting the color former solution thus obtained with an aqueous solution of a surface active agent and adding the resultant solution to a liquid gelatin silver halide emulsion prior to coating the latter upon a support.

3. The method of incorporating into a gelatin silver halide emulsion layer, a benzimidazole substituted color former selected from the class corresponding to the following formulae:

Rs C-Ri Ra C-Rr-(Rsh wherein R is a hydroxy aromatic radical, the hydroxy group being nucleary attached and said radical being linked to the benzimidazole nucleus in an ort-ho position to said hydroxy group; R is an alkyl chain of at least 10 carbon atoms; R is a water solubilizing group; R is a phenylene radical; R is the group -NH-COCH A in which A is selected from the group consisting of alkyloyl, aroyl, cyano and carbethoxy groups; n is selected from the class consisting of 1 and 2; R is selected from the class consisting of hydrogen, carboxyalkyl, allyl and lower alkyl groups; R, is selected from the class consisting of lower alkyl, allyl, aryl and heterocyclic groups; and X is a member selected from the class consisting of halogen and sulfo groups which comprise dissolving said color former in butyrolactone, diluting the color-former solution thus obtained with a water solution of a surface active agent and adding the resultant dispersion to a liquid gelatin silver halide emulsion prior to coating the latter upon a suitable support.

4. The method of incorporating a color former into a gelatin silver halide emulsion layer as defined by claim 1, wherein said color former is 2-(4'-benzoylacetaminophenyl) -1-octadecylbenzimidazole-S-sulfonic acid.

References Cited by the Examiner UNITED STATES PATENTS Ben-Ezra et a1. 96100 NORMAN G. TORCHIN, Primary Examiner. I. T. BROWN, Assistant Examiner.

Disclaimer 3,316,094.Aaron Ben-Ezra, Binghamton, NY. METHOD OF INCORPORAT- ING COLOR COUPLERS IN HYDROPHILIC COLLOIDS. Patent dated Apr. 25, 1967. Disclaimer filed Sept. 30, 1982, by the assignee, Eastman Kodak Co.

Hereby enters this disclaimcr to all claims of said patent.

[Offlcial Gazette April 5, 1983.] 

1. THE METHOD OF INCORPATING IN A LIGHT-SENSITIVE GELATIN HALIDE EMULSION, A COLOR FORMER FAST TO DIFFUSION AND CAPABLE OF FORMING UPON COLOR DEVELOPMENT WITH A PRIMARY AROMATIC AMINO DEVELOPING AGENT, A DYE IMAGE SELECTED FROM THE CLASS CONSISTING OF AZOMETHINE, INDOANILINE AND PHENAZONIUM DYE IMAGES, SAID COLOR FORMER CONTAINING A BENZIMIDAZOLE NUCLEUS CONNECTED THROUGH ITS CARBON ATOMS IN THE 2-POSITION TO THE RESIDUE OF THE COLOR-FORMING MOLECULE WHICH IS REACTIVE WITH THE OXIDATION PRODUCT OF A PRIMARY DEVELOPING AGENT AND WHICH CONTAINS A REACTIVE GROUP SELECTED FROM THE CLASS CONSISTING OF A REACTIVE METHYLENE AND PHENOLIC HYDROXY GROUP, SAID BENIMIDAZOLE NUCLEUS BEING SUBSTITUTED ON ONE OF THE NITROGEN ATOMS BY AN ALIPHATIC HYDROCARBON RADICAL CONTAINING AT LEAST 10 CARBON ATOMS AND SUBSTITUTED IN THE BENZENE PORTION BY A WATER SOLUBILIZING GROUP WHICH COMPRISES DISSOLVING SAID COLOR FORMER IN BUTYROLACTONE, DILUTING THE RESULTANT SOLUTION WITH AN AQUEOUS SOLUTION CONTAINING A SURFACE ACTIVE AGENT AND THEN ADDING THE RESULTANT DISPERSION TO THE LIQUID GELATIN SILVER HALIDE EMULSION PRIOR TO COATING IT UPON A SUITABLE SUPPORT. 